AU2007236402B2

AU2007236402B2 - Foundation structure

Info

Publication number: AU2007236402B2
Application number: AU2007236402A
Authority: AU
Inventors: Lars Bo Ibsen; Soren Andreas Nielsen; Bruno Schakenda
Original assignee: MBD Offshore Power AS
Current assignee: MBD Offshore Power AS
Priority date: 2006-04-10
Filing date: 2007-04-10
Publication date: 2012-05-17
Anticipated expiration: 2027-04-10
Also published as: WO2007115573A1; EP2010718B1; US7891910B2; KR20090010974A; EP2010718A1; CA2648859A1; US20090191004A1; BRPI0710056A2; BRPI0710056B1; LT2010718T; AU2007236402A1; CN101466900A; US20110200399A1; CA2648859C; KR101435219B1; DK2010718T3; PL2010718T3

Abstract

Method of installing a bucket foundation structure comprising one, two, three or more skirts, into soils in a controlled manner. The method comprises two stages: a first stage being a design phase and the second stage being an installation phase. In the first stage, design parameters are determined relating to the loads on the finished foundation structure; soil profile on the location of installation; allowable installation tolerances, which parameters are used to estimate the minimum diameter and length of the skirts of the bucket. The bucket size is used to simulate load situations and penetration into foundation soil, in order to predict necessary penetration force, required suction inside the bucket and critical suction pressures, which penetration force, required suction, and critical suction pressures are used as input for a control system in the second stage, in which second stage the pa- rameters determined in the first stage are used in order to control the installation of the bucket.

Description

1 Foundation structure Field of the Invention The invention concerns a method of installing a bucket foundation structure. 5 Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages or to provide a useful alternative. Summary of the Invention According to a first aspect of the invention there is disclosed herein a method of 10 installing a bucket foundation structure comprising one, two, three or more skirts, into soils of varying characteristics in a controlled manner, where the method comprises two stages: a first stage being a design phase and the second stage being an installation phase, such that in the first stage, design parameters are determined relating to the loads on the finished foundation structure; soil profile on the location of installation; allowable 15 installation tolerances, which parameters are used to estimate the minimum diameter and length of the skirts of the bucket, which bucket size is used to simulate load situations and penetration into foundation soil, in order to predict necessary penetration force, required suction inside the bucket and critical suction pressures, which penetration force, required suction, and critical suction pressures are used as input for a control system in the second 20 stage, in which second stage the parameters determined in the first stage are used in order to control the installation of the bucket; and further that sensors provided in the installation equipment, such as pumps, conduits and on the structure, feeds input to the control system, where the input from the sensors are compared to the parameters derived from the first stage, and that the control system activates and/or deactivates different 25 means arranged in and around the bucket foundation structure for creating the penetration force needed. Preferably the bucket foundation structure has one, two, three or more skirts, and that the skirts define a lower rim of the bucket structure, as seen in the use situation, and 30 that further a plurality of apertures or nozzles interconnected with appropriate conduits are distributed along the lower rim of the bucket structure, such that a flow and/or jets of media, such as a fluid, gas, air, steam may issue from the apertures or nozzles.

la Preferably the apertures and/or nozzles are arranged in attachments in the shape of one or more chambers provided along at least part of the lower rim of the bucket structure. 5 Preferably the pressures and media flows are controlled according to input from the first stage by controlled manipulation of valves and pumps, for example positive displacement pumps, in accordance with the control parameters loaded into the control system. 10 Preferably the control system during the second stage controls the penetration of the structure by activating control actions such as creating one or more of the following: constant flow of media in one or more chambers or conduits; constant pressure established by a media in one or more chambers or conduits; variations of flow or pressure established by a media in one or more chambers; Is pulsating flow and/or pressure established by a media in one or more chambers or conduits. Preferably the sensors are selected among the following: transducers, inclinometers, accelerometers, pressure sensors. 20 Preferably the second stage is either manually operated, semi-automatically or fully automatically operated by means of computers. Preferably the method includes a system wherein three or more winches are 25 arranged on an upper part of the foundation, where a wire is arranged between the winches and pre-installed anchors, where said anchors are arranged substantially equidistant radially around the foundation structure, and where the winches may be activated in order to reel in or reel out wire in response to data from the control system, whereby the system provides additional guidance control for the placing of the foundation 30 structure in the second stage. Brief Description of the Drawings Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompany drawings wherein: FIG. I shows the foundation structure.

lb FIG. 2 shows the design phase. FIG. 3 shows the installation phase. FIG. 4 is a graph showing the prediction. FIG. 5 shows the result of Cone Penetration Test (CPT). 5 FIG. 6 shows the Bucket foundation. FIG. 7 shows the correction deformation of the bucket approximate by an equivalent deformation. FIG. 8 shows the failure of bucket subject to combined horizontal and moment loading in laboratory test. 10 FIG. 9 shows failure mode. FIG. 10 shows a cutout of the principle to determine effective area. FIG. 11 shows the principle to determine effective area. FIG. 12 shows the presentation of operation and control data. FIG. 13 shows the foundation structure with anchors and cables. is Description of Preferred Embodiment The method of an embodiment of the invention is employed to install a foundation structure (1), see fig. 1, consisting of one, two, three or more skirts, into soils (5) of varying characteristics in a controlled manner (fig.1). The method finds use either in a seabed or an onshore location where the soil is beneath ground water level. The skirt 20 can be constructed of sheet metal, concrete or composite material forming an enclosed structure of any open-ended shape used for e.g. bucket foundation, monopiles, suction anchors or soil stabilisation constructions. The method is based on a design phase (fig. 2) and an installation phase (fig. 3) 25 which is the basis for controlling the suction pressure in the enclosure and the pressures and flows along the lower perimeter/rim (edge) (4) of the skirt while penetrating the foundation structure into the soil (5). Embodiments of the invention make it possible to control penetration e.g. suction 30 anchors or bucket foundations into the seabed soil even if the soil consists of impermeable layers where it is not possible to establish a flow of water (seepage) around the rim by means of under pressure in the interior of the structure. The main structure is designed to absorb the different forces and loads which is 35 applied during the installation process and during the operation of the facility, that is to 1c say all the forces and loads the structure is intended and designed to withstand during the operational lifetime of the said facility. An attachment along the rim of the skirt consists of one or more chambers, 5 typically four, with nozzles where pressure and/or flows of a media, e.g. fluid, air/gas or steam, can be established in a controlled manner through said chambers and nozzles, resulting in the reduction of the shear strength in the soil in the near surroundings of the rim WO 2007/115573 PCT/DK2007/000178 2 and/or skirt. The pressures and flows can be controlled by means of valves or positive displacements pumps (3) for one, more or all chambers during the placement, i.e. while the structure is lowered into the soil. The invention ensures that the penetration speed and the inclination of the construction are controlled within the design require 5 ments. The chamber(s) at the rim (4) can be established in the form of a pipe work fitted along the rim with drilled or fitted nozzles pointed in the desired direction(s). The pipe work is connected through risers to a central manifold supplied with the media at a 10 sufficient flow and pressure. Each riser section is fitted with a controlling device (3) regulation flow and pressure. As an optional feature, see fig. 13, the main structure can be fitted with a system com prising three or more electrically and/or hydraulically operated winches (34) which are 15 connected to preinstalled anchors (36) by wires (35). When the three winches con nected to separate anchors are used, they are arranged with approximately 1200 be tween them, such that they radially extend into different directions. By simply manipu lating the winches either alone or in co-operation it is possible to adjust the inclination of the foundation. This system can be used as redundant or excess control measure of 20 the inclination in case of extreme environmental parameters such as high waves or if the rim pressure system is not available for any reason. The operation of the winches can introduce a horizontal force in the opposite direction of an inclination as a correc tive action. 25 The main structure is fitted with transducers for monitoring and logging purposes: The pressure inside the enclosure (23), the vertical position (24) and the inclinations (26) and (27). The transducers are connected to a central control system (15). 30 The pipe work on the rim can be of greater, equal or less dimensions than the thick ness of the rim. QI IRTITI ITF= WFF=T 1I1 II F= 9AI WO 2007/115573 PCT/DK2007/000178 3 In the inside of the bucket structure an under pressure may be created. This may be established by activating an evacuation pump creating suction i.e. a lower pressure inside the bucket structure than outside the structure. 5 The method consists of two stages: - Prediction of the penetration forces, called the design phase (fig. 2). - Control of the penetration in accordance to the prediction, called the installation phase (fig. 3). 10 The method is an integrated approach with regards to the design of the said foundation structures and is based on the calculation and simulation of the precise position of each individual foundation structure with respect to physical in-situ parameters as foundation position and soil characteristics at the particular installation location. 15 The prediction (14) represented by a diagram, (fig. 4), showing the calculation of the needed penetration forces (31), the available suction pressure (32) and the maximum allowable suction pressure not causing ground or material failure (33) in accordance to the design code in question. 20 The calculation is based upon the soil characteristics gained from interpretation of data obtained by a CPT investigating (CPT=cone penetration test), (fig. 5), the dead weight of the structure, the water depth and the load regime. The input data are evaluated and transformed into the design parameters (7), called the design basis. 25 The load analysis (8) is an analytical and/or numerical analysis which determines the physical size of the bucket, diameter and skirt length, based on a design methodology using a combination of earth pressure on the skirt and the vertical bearing capacity of the bucket. 30 If the bucket foundation is regarded as two cramp walls where it is possible to develop stabilizing earth pressures on the front and back side of the foundation, an analytical model for the design of a bucket foundation with the diameter D and a skirt depth of d can be used.

WO 2007/115573 PCT/DK2007/000178 4 The earth pressure action on the bucket, with a skirt depth of d is assumed to rotate as a solid body around a point of rotation 0 found in the depth dr, below the soil surface. The mechanism of the earth pressure and reaction of the bearing capacity for the point 5 of rotation is either anticipated to be placed below the foundation level (fig. 6a), or anticipated to be placed above the foundation level (fig. 6b). If the bucket foundation is assumed built of two cramp walls where it is possible to develop a stabilizing earth pressure on the front and back side of the foundation the earth pressures can be calcu lated with the following approximation. In traditional calculations for vertical walls 10 the point of rotation is found in the plane of the wall, which in this case is not feasible. Thus, the deformation of the bucket is described by two parallel walls with a point of rotation corresponding with the fact that these points are found in the plane of the wall, (fig. 7) shows the equivalent mode of rupture. 15 Unit earth pressure may generally be calculated as: e'=7'zK 7 +p'K,+c'K. (1) Since the bucket is circular with extension D perpendicular to the horizontal force H's and founded in friction soil c = c'= 0 , the total earth pressure E' is written as: 20 E' = (orK, ) D (kN per m skirt lengt) (2) where o',, is the vertical effective stress in the level in question. For z ~ 0 i.e. by the soil surface, K, corresponds to rupture zones on both sides of a rough wall (plan case) and may be written as: 25 Kq (Z ~t 0) = K,, = K,'' - Kr" (3) applying superscription p and a for passive and active earth pressure and r for rough wall. If Rankine's earth pressure is applied it is not possible to find an exact expres sion forK,. However, the following equations have been found to describe the exact 30 calculated K,- values with an accuracy which is better than 0,5 %, Hansen. B (1978.a): WO 2007/115573 PCT/DK2007/000178 5 K pr =Kp +0,007(e 9 ""n" -1) 7 P (4) Kr = K," - 0, 007(1- e- ") where KP =(l+sin p)e 2 _(5-(5) K," =(1-sin p)e 2 A bucket foundation exposed to a combined moment and horizontal load shows a dis 5 tinct spatial rupture zones, (fig. 8). Den spatially influence around the bucket can be interpreted as a active diameter D > D of the bucket on which the earth pressure may act from the plane state. In this case the absolute size of the earth pressure may, ac cording to (2) and (3), be written: 10 E' =aoK,,PiD (6) the active diameter is given by: D=D+0,25dsin 4j+ ) (7) 42) The absolute size of the earth pressure is a function of the depth z and assumed to be 15 independent of the position of 0. It is possible once and for all to calculate it as the difference between passive and active earth pressure on a rough wall rotating around its lowest point. (Fig. 6b) shows that the earth pressures are assumed to change from active to passive in the level of the bucket's rotation point. As a reasonable, permissi ble static approximation, (6) may be applied to calculate the difference. 20 E'd= El'E-(8)

E

1 and E 2 may with approximation be calculated separately, (3), changing between active and passive earth pressure when passing the level of 0. The shear forces 1 25 andF2 acts stabilizing. If 0 is located entirely below the surface of the foundation the shear forces may be calculated in the usual manner, since the vertical foundation sur faces are assumed as a rough wall: WO 2007/115573 PCT/DK2007/000178 6 F = E, tan (o -F2= E 2 tan 9 (9) However, if the location of 0 is above the foundation surface, this calculation will be on the unsafe side. A calculation on the safe side corresponding to the calculating of E applying (2) - (6) consists of calculation the following summation: 5 d =F+2Egtanp (10) This is directly incorporated into the vertical equilibrium equation. In the moment equation, around the point on the centre line of the foundation it is incorporated with moment lever D /2. 10 When calculating the bearing capacity of the bucket the first calculation must deal with the different rotation points located on the symmetric line of the bucket. The earth pressures as well as the external forces VI,H,,I 1M,,) must be converted to 3 resultant components of forces at the bottom of the bucket, (fig. 6). This is done by 15 requiring vertical, horizontal, and moment equilibrium. Horizontal: Hd = H,,,-Ed (11) Vertical: 20 V( V2, -F) where

V,

1

,

1 ,+(V + V, )R Vnoite is the weight of the wind turbine (Vi+)) (Vie + V; is the bucket's weight of iron and soil reduced for buoyancy 25 Moment: M =M,,+ H,,,d + E2(d -z2 )- El(d-zl)-Fd D 2 (13) Concerning the bearing capacity at the bottom of the foundation it should be noted that it is characterized by a large eccentricities e, and a large q-part described by q/yb WO 2007/115573 PCT/DK2007/000178 7 The permissible load; Hd is obtained by the earth pressure Ed and the shear force Sd which in this case may be calculated from: Sd Vd tan Pd (14) 5 To ensure against rupture due to sliding the following inequality must be complied with: Hd Sd+Ed (15) 10 Furthermore it must be demonstrated that there is sufficient safety against bearing ca pacity rupture: V, ! Rd (16) In a normal bearing capacity rupture as shown in (fig 9a), the general bearing capacity equation: Rd= 1 7'b'NY i, +q'Nq iq 15 1 2b ' ± q (17) may be used assuming that b'/l is so close to zero, that all shape factors can be set equal to 1. No depth factor is used since El and F both are included when consider ing the equilibrium of the foundation. This rupture corresponds to a point of rotation 0 20 below skirt level, i.e. El is a complete passive earth pressure and E 2 a complete active earth pressure. The dimensionless factors N and i are determined from the equations below, by using the permissible plane friction angle 9 d. N, = ((Nq -1)cos (d)2 N = e"tand 1+sind N q 1-singd (18) = 1 , i' q iq = 1_ Hd~ (19) V + A' Cot (0d (19) WO 2007/115573 PCT/DK2007/000178 8 If e becomes sufficiently large, an alternative rupture is found which may be much more dangerous, (fig. 9b). This rupture has proven to be possible if e > e', where D 0, 45 sin(1, 5 (Pd) (20) 5 The corresponding bearing capacity may be written: R d 1 r A 2 r(21) where: Ny x2N ie +3 Hd Vd (22) 10 It is noted that the horizontal force Hd , pointing towards the edge of the skirt now acts stabilizing. On the other hand there is no q-led, because the line failure tenninates un der the bucket. The effective area A' used in the bearing capacity equation is the area in the skirt dept 15 d and is calculated as twice the area of the segment of a circle, which passes V through d . Afterwards A is transformed to a rectangle with the identical area (fig 10): Vd A'= r2(V7r i-sinv) =b'' 180 v=2arccos(e b'~ tanT A'=1 ,7(r -e) '= A b' (23) 20 In the method of calculating the moment capacity of the bucket, a precise calculation of earth pressure and bearing capacity for the bucket demands that the kinematical WO 2007/115573 PCT/DK2007/000178 9 conditions have been complied. The point of rotation 0 which is the centre of the line failure in (fig 9b) must also be the point of rotation used in the earth pressure calcula tion, (fig. 6b). However, a precise calculation on these conditions is extremely compli cated. For the detennination of this moment capacity for a bucket with fixed dimen 5 sions D, d and Vm the following statically permissible method of approximation, is in accordance to / Hansen. B (1978.b)/ and is on the safe side. The largest moment capac ity is obtained if Ed is utilized to the full depth (identical stabilizing force, but larger moment): 10 1. O's level (Pressure jump) is chosen so that Hd = 0 at the bottom of the founda tion 2. It is controlled that the bearing capacity of the line failure is the most critical. 3. If not 0 must be raised by increasing Hua. 15 4. M,,, =H,(h+hk,) 5. The moment capacity of the bucket has been reached when Hunt has been in creased so much that V =Rd, where Rdhas been determined by the equation (21). 6. As control the following calculation has been made: 20 H,1 = Sd + Ed (24) M, =Rd e + Fd -- + E(d - z 1 )- H,d - E 2 (d - z 2 ) 2 (25) With small loadings the resulting load at the lower edge of the foundation will adopt negative values. This is caused by the fact that the passive earth pressure exceeds the 25 external load. As the passive earth pressure cannot act as a driving force, the following requirements to the resulting loads as well as eccentricity are introduced: Hd < H , Vd > 0 D 2 (26) WO 2007/115573 PCT/DK2007/000178 10 The input data for the load analyses is the design parameters (7). The analysis process is perfonned using formulas and methods based on series of tests on scale buckets varying from 0100 mm to 02000 mm in diameter. The ability of the structure/soil 5 interaction to handle the load regime, e.g. static load and dynamic load, is evaluated. If the safety level stipulated in the design code in question, is not within the given limits, the diameter and /or the length of the bucket respective skirt are increased (10), and the load analyses is repeated. 10 If the safety level is within the limits given in the design codes, the penetration analy sis (11) is performed with the calculated bucket size. The calculation follows the de sign procedure of a traditional, embedded gravity foundation. The gravity weight of the foundation is primarily obtained from the soil volume enclosed by the pile, yield ing also an effective foundation depth at the skirt tip level. The moment capacity of 15 the foundation is obtained by a traditional, eccentric bearing pressure combined with the development of resisting earth pressures along the height of the skirt. Hence, the design may be carried out using a design model that combines the well-known bearing capacity formula with equally well-known earth pressure theories. The foundation is designed so that the point of rotation is above the foundation level, i.e. in the soil sur 20 rounded by the skirt and the bearing capacity. Rupture occurs as a line failure devel oped under the foundation. The ability to penetrate the foundation into the soil is evaluated (12). If the bucket can not be penetrated within the parameters given in the prediction, (fig. 4), the bucket 25 diameter is increased (13) and the load analyses (8) are repeated. This design stage is called conceptual design. The prediction is presented in a graphic diagram, (fig.4), to be used by the detailed design for the construction of the foundation structure and for the installation process. 30 The prediction is presented as an operation guideline used by the operators or is feed directly to a computerized control system as data input.

WO 2007/115573 PCT/DK2007/000178 11 The prediction includes parameters for the penetration force, the critical suction pres sure which will cause soil failure, critical suction pressure which will cause buckling of the foundation structure, available suction pressure due to limitations in the pump system as a function of the penetration depth. 5 The installation of the said foundation structures is a controlled operation of the pene tration process. The operation of the control system (15) is performed either manually, semi automatically or fully automatically based upon interpretation of the above mentioned data (14). In order to automate the process partly or fully investments must 10 be made in suitable equipment, but any step in the process may be carried out by man ual means. The control is performed based on readings of the actual penetration depth and inclination of the structure by high accuracy instruments. The control action can be introduced into the soil (5) in different modes: 15 0 Constant flow of media in one or more chambers (4). * Constant pressure established by a media in one or more chambers (4). e Variations of flow or pressure established by a media in one or more chambers (4). " Pulsating flow/pressure established by a media in one or more chambers (4). 20 The mode is selected in accordance with the prediction, depending of the properties of the soil e.g. grain size, grain distribution, permeability. The soils reaction to the initiated control actions is either reduction of the shear 25 strengths at the rim of the skirt (30) or reduction of the skin friction on the skirt sur face or a combination of both. The control system (15) consists of elements illustrated in the flow diagram (fig. 3) and example of the user interface regarding actual readings (fig. 12). 30 Input elements are the measuring devices for the vertical position (24), the inclination in X-direction (26), the inclination in Y-direction (27) and the pressure inside the bucket, e.g. suction pressure (23).

WO 2007/115573 PCT/DK2007/000178 12 Output elements are data to regulate the suction pressure (16), data to regulate the in dividual pressure/flow (17) in one or more chambers at the skirt rim (4) and data for the event recording (18) for the verification of the installation process. 5 An optional output element is data to operate the optional winches (34), see fig. 13. The alternative or additional system comprising winches is explained above. Different control routines are implemented in the control system to initiate the actions 10 ensuring the installation process to be within the predicted tolerances. As a minimum three routines are needed, 1) verification of vertical position (19), 2) verification of penetration velocity/suction pressure (20) and 3) verification of inclination (25). The sequence of the control routines can be arranged to suit the actual installations situa tion. 15 The routine for vertical position (19) measures the vertical position (24) of the struc ture with reference to the seabed, if the position is within the tolerances of the finial level; say +/- 200 mm, the installation procedure is finalized. 20 The routine for verification of penetration velocity/suction pressure (20) measures the vertical position (24) with a sampling rate sufficient to calculate the penetration veloc ity. The installation process is started in a mode with no pressure/flow in the chambers at the rim (4). If the rate of penetration is below the minimum level, say < 0,5 m/h, the suction pressure is increased (22). The suction pressure is measured (23); the suction 25 pressure must be kept below the safety level for soil failure, say 60% of the critical suction pressure calculated in the prediction. If the suction pressure is at the maximum level and the penetration velocity is not increased, the control mode is changed (21) to constant or pulsating pressure/flow in the entire chambers (4). 30 The verification of inclination (25) measures the inclination in the X- direction (26) and the Y-direction. If the inclination is not within the tolerances stated in the design basis, corrective action is initiated (28). If running in the control mode with no pres sure/flow in the chambers (4), the control device (3) in the sector of the same direction 13 as the desired correction is activated. If running in the control mode with constant/pulsation pressure/flow in the chambers (4), the control device (3) in the opposite sector of the direction as the desired correction is deactivated. An optional control measure can be initiated by operating the winch system (34). 5 Preferred features of using the said methodology is three fold compared the normal used methods for placing skirted foundations/anchors: Penetration to a greater depth using less penetration force for a given physical 10 dimension of the embodiment without disturbing the overall soil conditions and strength is achieved. Penetration of this type of foundation structures in permeable layers beneath layers of impermeable material e.g. silt/soft clay is possible. 15 The ability to control the inclination of the foundation structure during the penetration process is assured. Example of use 20 The bucket foundation can be used for e.g. offshore based wind farms where the wind turbines or metrology masts are mounted on a foundation structure provided in the seabed. The application of the bucket foundation can be facilitated in a variety of site locations and load regimes in the range as follows: 25 Seabed soils: Loose to very dense sand and/or soft to very stiff clays. Water depth: 0 - 50 m Load regime: Vertical loads: 500 - 20.000 kN Horizontal loads: 100 - 2.000 kN Overturning moment: 10.000 - 600.000 kNm 30 An example of a typical bucket foundation for offshore wind turbine installation is shown in (fig. 11). The overturning moment at seabed level is 160.000 kNm, vertical load is 4.500 kN and horizontal load is 1000 kN.

WO 2007/115573 PCT/DK2007/000178 14 The seabed consists of medium dense sand and medium stiff clay. The foundation structure consists of a bucket with a diameter of 11 m and a skirt 5 length of 11,5 m and a total height over seabed of 28 m. The overall tonnage of the foundation structure is approximately 270 tons. The thickness of the steel sheet mate rial is 15 -60 mm in the various part of the structure. The skirt is penetrated into the seabed with a velocity of 1-2 m/h giving an overall 10 installation time for the foundation of 18 -24 hours exclusive of work for scour protec tion if needed.

Claims

1. Method of installing a bucket foundation structure comprising one, two, three or more skirts, into soils of varying characteristics in a controlled manner, where the method comprises two stages: a first stage being a design phase and the second stage being an installation phase, such that in the first stage, design parameters are determined relating to the loads on the finished foundation structure; soil profile on the location of installation; allowable installation tolerances, which parameters are used to estimate the minimum diameter and length of the skirts of the bucket, which bucket size is used to simulate load situations and penetration into foundation soil, in order to predict necessary penetration force, required suction inside the bucket and critical suction pressures, which penetration force, required suction, and critical suction pressures are used as input for a control system in the second stage, in which second stage the parameters determined in the first stage are used in order to control the installation of the bucket; and further that sensors provided in the installation equipment, such as pumps, conduits and on the structure, feeds input to the control system, where the input from the sensors are compared to the parameters derived from the first stage, and that the control system activates and/or deactivates different means arranged in and around the bucket foundation structure for creating the penetration force needed.

2. Method according to claim 1 wherein the bucket foundation structure has one, two, three or more skirts, and that the skirts define a lower rim of the bucket structure, as seen in the use situation, and that further a plurality of apertures or nozzles interconnected with appropriate conduits are distributed along the lower rim of the bucket structure, such that a flow and/or jets of media, such as a fluid, gas, air, steam may issue from the apertures or nozzles.

3. Method according to claim 2, wherein the apertures and/or nozzles are arranged in attachments in the shape of one or more chambers provided along at least part of the lower rim of the bucket structure.

4. Method according to claim 1, wherein the pressures and media flows are controlled according to input from the first stage by controlled manipulation of valves and pumps, for example positive displacement pumps, in accordance with the control parameters loaded into the control system. 16

5. Method according to claim 1, wherein the control system during the second stage controls the penetration of the structure by activating control actions such as creating one or more of the following: constant flow of media in one or more chambers or conduits; constant pressure established by a media in one or more chambers or conduits; variations of flow or pressure established by a media in one or more chambers; pulsating flow and/or pressure established by a media in one or more chambers or conduits.

6. Method according to claim 1, wherein the sensors are selected among the following: transducers, inclinometers, accelerometers, pressure sensors.

7. Method according to claim 1, wherein the second stage is either manually operated, semi-automatically or fully automatically operated by means of computers.

8. Method according to claim 1, wherein a system comprising three or more winches are arranged on an upper part of the foundation, where a wire is arranged between the winches and pre-installed anchors, where said anchors are arranged substantially equidistant radially around the foundation structure, and where the winches may be activated in order to reel in or reel out wire in response to data from the control system, whereby the system provides additional guidance control for the placing of the foundation structure in the second stage.

9. Method of installing a bucket foundation structure substantially as hereinbefore described with reference to the accompany drawings. Dated 30 April, 2012 MBD Offshore Power A/S Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON